title: Incidence of second primary malignancies during a long-term surveillance of patients with differentiated thyroid carcinoma in relation to radioiodine treatment.
abstract: OBJECTIVE
  Controversies remain over the actual risk of developing a second primary malignancy (SPM) as a consequence of I-131 treatment in patients with differentiated thyroid carcinoma (DTC). The objective of this study was to evaluate the adjusted rate and risk estimate of SPM in radioiodine-treated patients after controlling for confounding factors.
  
  
  METHODS
  A retrospective cohort study was conducted on 973 cases randomly selected from a population of 9550 radioiodine-treated DTC patients. The cases with prior or coincident nonthyroid malignancies and those with SPM during the first 3 years of the initial I-131 treatment were not included. Age-standardized rate of SPM and its 95% confidence interval (CI) during a median of 6 (3-26) years follow-up in DTC patients was compared with that of the general population. A logistic multivariable analysis was also conducted to identify the potential covariate factors that might influence the risk of SPM.
  
  
  RESULTS
  Eleven patients from 7370 person-years at risk developed an SPM. The standardized rate ratio of nonthyroid malignancy was 0.81 (95% CI, 0.57-1.04) for the studied patients relative to the general population. The cumulative dose of I-131 more than 40 GBq (1.08 Ci) was the sole factor associated with increased odds of SPM, after adjusting for age, follow-up duration, histology of DTC, presence of metastasis, and history of external radiotherapy (odds ratio, 113; 95% CI, 8.6-1495.6; P < 0.0001).
  
  
  CONCLUSIONS
  The overall rate of SPMs was not significantly increased after a minimum interval of 3 years from the first I-131 treatment; however, the chance of this event may be radically increased in patients who had received a cumulative activity of I-131 exceeding 40 GBq (1.08 Ci).
authors.affiliation: Research Institute for Nuclear Medicine, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Babak
authors.initials: B
authors.lastname: Fallahi
authors.forename: Khadijeh
authors.initials: K
authors.lastname: Adabi
authors.forename: Mahnaz
authors.initials: M
authors.lastname: Majidi
authors.forename: Armaghan
authors.initials: A
authors.lastname: Fard-Esfahani
authors.forename: Ramin
authors.initials: R
authors.lastname: Heshmat
authors.forename: Bagher
authors.initials: B
authors.lastname: Larijani
authors.forename: Vahid
authors.initials: V
authors.lastname: Haghpanah
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002454:Cell Differentiation; D002648:Child; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000009:adverse effects* / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D009381:Neoplasms, Radiation-Induced / Q000453:epidemiology*; D016609:Neoplasms, Second Primary / Q000453:epidemiology* / Q000209:etiology; D012189:Retrospective Studies; D018570:Risk Assessment; D013964:Thyroid Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D013997:Time Factors; D055815:Young Adult
chemical_list: D007457:Iodine Radioisotopes